Preparation of naphthalene and dimethylnaphthalenes



United States Patent 3,153,675 PREPARATION OF NAPHTHALENE AND DIMETHYLNAPHTHALENES Joseph C. Mason, .hu, Ciaymont, Del., assignor to Sun Oil Company, Philadelphia, Pa, a corporation of New Jersey Filed June 27, 1961, Ser. No. 119,848 6 Claims. (Cl. 260-668) This invention relates to the preparation of condensed ring dicyclic aromatic hydrocarbons from charge stocks derived from gas-oil and more specifically concerns an integrated process for producing naphthalene and 2,6- and 2,7-dimethylnaphthalenes.

Petroleum fractions which boil within the range of 400-550 F. generally contain substantial amounts of alkylnaphthalenes, such as mono-, di-, and trimethylnaphthalenes and in smaller quantity, the ethylnaphthalenes. Recycle fractions, which are formed in the cracking of petroleum stocks and which include this boiling range, often contain major proportions of aromatic hydrocarbons that are mainly alkylnaphthalenes. Such fractions typically may have aromatic contents varying within the range of 25-97% but usually contain between 50% and 95% aromatics depending upon the particular operation in which the petroleum fractions are produced. These hydrocarbon charge stocks are obtained in both catalytic and thermal cracking processes and in operations in which combinations of catalytic and thermal cracking steps are utilized. Stocks having high alkylnaphthalene contents can also be obtained by extracting straight run petroleum fractions of appropriate boiling ranges, such as kerosene, or catalytic fractions such as catalytic gas-oil, with solvents, such as furfural or sulfur dioxide, or by selective adsorption with silica gel. These aromatic concentrates may contain up to 100% aromatic hydrocarbons.

The present invention is directed to the preparation of naphthalene and 2,6- and 2,7-dimethylnaphthalenes from aromatic hydrocarbon charge stocks which comprise a mixture of alkylnaphthalenes and which can be derived from such sources as referred to above. The charge stock boils mainly within the range of 440525 F. and preferably is composed mainly of alkylnaphthalenes in which the allcyl groups appear at both the alpha and beta positions on the naphthalene nucleus.

It has been proposed heretofore to prepare naphthalene by subjecting aromatic hydrocarbon stocks containing a kylnaphthalenes to high temperature dealkylation in the presence of hydrogen. As a general rule, the dealkylation conditions employed can effect only a partial dealkylation in one pass of the alkylnaphthalenes through the reactor. In order to increase the yield of naphthalene, it is desirable to fractionate the reaction product to obtain the desired naphthalene product and also to recover another fraction comprising unconverted and only partially converted alkylnaphthalenes. The recovered alkylnaphthalenes can be recycled to the dealkylator to effect further conversion.

Percent fl-Methylnaphthalene 70 a-Methylnaphthalene 15 Dimethylnaphthalenes 15 According to the present invention, this material is utilized sufficient to etfect dealkylation of alkynaphthalenes.

in a way to produce, as additional products, 2,6- and 2,7- dimethylnaphthalenes which are useful intermediates for the preparation of resins.

The invention is described more specifically with reference to the accompanying drawing which is a schematic flowsheet illustrating a combination process for producing naphthalene and 2,6- and 2,7-dimethylnaphthalenes from a hydrocarbon stock containing alkylnaphthalenes.

The process as illustrated in the drawing involves a preliminary catalytic hydrocracking-desulfurization step adapted to condition the alkylnaphthalene charge material prior to a high temperature dealkylation step for producing the naphthalene. The charge, which enters the system through line 10, is a gas-oil fraction boiling in the range of 440525 F. and containing alkylnaphthalenes, and preferably is a catalytic gas-oil aromatic extract containing a major proportion of dicyclic aromatics together with a minor proportion of aromatics having only one aromatic ring and only a small amount or no saturated hydrocarbons. For example, a preferred charge may contain 60% dicyclic aromatics, 35% monocyclic aromatics and 5% saturates.

The heated charge, together with hydrogen from line 11 and material hereinafter specified from line 34, passes through line 12 to a catalytic desulfurizer-hydrocracker 13 which contains a desulfurization catalyst such as cobalt molybdate on alumina or molybdenum disulfide on alumina. The conditions for conducting this catalytic conditioning step include a temperature within the range of 800980 F., a pressure of -1000 p.s.i.g., with a range of 200500 p.s.i.g. preferred, a hydrogen to hydrocarbon mole ratio of 3:1 to 25:1 and preferably 5:1 to 15:1, and a liquid hourly space velocity of 0.5 to 10 (volumes of charge per hour per bulk volume of catalyst). The hydrogen consumption under these conditions should be between 65-500 s.c.f. per barrel of liquid feed per percent sulfur in the feed and preferably between 200 and 400 s.c.f. per barrel. This conditioning step effects cracking of most of the saturates and some of the monocyclic aromatics and also converts most of the sulfur in the hydrocarbon stock to hydrogen sulfide. It also effects cracking of diaryl methanes in the stream from line 34-, as hereinafter more specifically described.

From hydrocracker 13 the reaction product is sent through line 14 to fractionator 15 from which normally gaseous components are removed overhead through line 17 and a C -400" F. gasoline fraction is obtained from line 18. The 400+ P. fraction which contains the alkvlnaphthalenes is removed via line 16.

Referring now to the high temperature dealkylation step, a stream of material, obtained as hereinafter specified and composed mainly of monomethyl and dimethylnaphthalenes and a small amount of ethylnaphthalenes, passes through line 20 together with hydhrogen introduced via line 19 into dealkylator 21. In the preferred embodiment the dealkylation is effected thermally without a catalyst. The conditions for this operation include a pressure of 1501000 p.s.i.g., preferably 200- 500 p.s.i.g., a hydrogen to hydrocarbon mole ratio within the range of 3:1 to 25:1 and preferably 5:1 to 15:1, a residence time of 2300 seconds with a preferred residence time of 1060 seconds, and a temperature above 1000 F., preferably within the range of 1200-l400 F., In this reaction only a partial dealkylation occurs and the alkyl groups which are in the alpha position on the naphthalene nucleus are removed at about twice the rate as those in the beta position. Hence the reaction product which leaves the reactor through line 22 contains, in addition to the desired naphthalene, unreacted naphthalenes and partially dealkylated naphthalenes, and

the alkylnaphthalene portion of the mixture is enriched with respect to beta alkyl groups as compared with the charge material fed to dealkylator 21.

, Alternatively, the dealkylation reaction can be effected catalyt cally utilizing a desulfurizing catalyst such as cobalt moiybdate or molybdenum disulfide. The presence of the catalyst in this step facilities the dealkylation reaction and in some cases permits it to be carried out at a lower temperature than that required for thermal dealkylation. The catalyst also effects the conversion of any remaining sulfur into hydrogen sulfide and hence permits the preparation of naphthalene having negligible sulfur content. The conditions for the catalytic dealkylation step include a pressure of 150-1000 p.s.i.g. with a range of 200-500 p.s.i.g. preferred, a hydrogen to hydrocarbon mole ratio of 5:1 to 25:1, a liquid hourly space velocity of 0.2-5.0, and a temperaturabove 1000" F., usually between 1100 F. and 1200 F., sufiicient to dealkylate alkylnaphthalenes and convert any remaining sulfur mainly into hydrogen sulfide.

The reaction product from line 22 passes to fractionator 23 from which gases and a C -400 F. aromatic gasoline cut are removed, respectively, from lines 26 and 25. The desired naphthalene product is taken from line 24 as material boiling in the 400450 F. range. Typically this fraction is composed predominantly of naphthalene and has a freezing point of 78.6 C. and a sulfur content that is practically negligible.

The 450+ F. material withdrawn from fractionator 23 via line 28 is composed mainly of monorncthyl and dimethylnaphthalenes with the alkyl groups in the beta position predominating. This stream also contains a small amount of material boiling above dimethylnaphthaleues which desirably should be removed. The stream is passed through line 28 to fractionator 29 from which a monomethylnaphthalene concentrate boiling in the range of 450500 F. is obtained overhead through line 30, a dimethylnaphthalene concentrate boiling 500520 F. is removed through line 31 and the higher boiling material is removed as bottoms via line 32.

The monomethylnaphthalene concentrate from line 30 typically is composed of about 82% B-methylnaphthalene and 18% a-methylnaphthaleue. According to the in vention, this material is converted in reactor 33 to diarylmethanes which are precursors for the subsequent formation of 2,6- and 2,7- dimethylnaphthalenes. This is done by the so-called formalite reaction in which the methyL naphthalene is reacted with formaldehyde or paraformaldehyde in the presence of an acid catalyst such as formic acid or sulfuric acid. This type of reaction has been described by Gordon et al., Ind. & Eng. Chem, Vol. 51, No. 10, pps. 1275-1278, October, 1959. The reaction proceeds in the following manner:

Under some conditions, this condensation reaction will proceed beyond the stage shown in the equation and result in the formation of resinous material containing more than two naphthalene nuclei. For the present purpose (ACID) it is preferred to stop the reaction at the stage shown in the equation, although this is not essential for practicing the invention since any resins that are formed subsequently will crack in the same manner as here-after described for the diarylmethanes. Control of the forrnalite reaction can be achieved largely by regulating the acid strength of the catalyst. For example, when formic acid is used as the catalyst, the product shown in the equation can be obtained by utilizing aqueous acid containing about 7080% by weight of formic acid.

The formalite reaction, which is effected in zone 33, preferably is carried out by mixing the monomethylnaphthalene concentrate from line with an appropriate amount of formaldehyde, introduced as indicated by line 34, and refluxing the mixture for several hours with a relatively large amount of aqueous formic acid having an acid strength of about 77%. The amount of formaldehyde used preferably is no greater than the stoichiometric amount required to react with only the fimethylnaphthalene present in the concentrate as per the foregoing equation. After refluxing for a suitable time, the mixture is then allowed to settle and the hydrocarbon phase is separated from the catalyst phase. Any formic acid remaining in the hydrocarbon phase can be removed by water washing or stripping. During the reaction the acid catalyst becomes diluted by the water formed in the reaction. The catalyst can be regenerated by distilling out the water formed during the reaction, leaving as residue a formic acid-water azeotrope containing about 77.4% acid by weight (B.P.=l07.2 C.) which can be re-used for effecting reaction of further amounts of the monomethylnaphthalene concentrate.

The reaction product from the formalite reaction is the material which is passed through line 34 for admixture with the fresh charge to desulfurizenhydrocracker 13. It has been found that the diarylmethanes formed in reactor 33 will, under the desulfurizing conditions described for zone l3, crack into monomethylnaphthalenes and dimethylnaphthalenes. The latter are mainly compounds having the methyl groups on opposite rings of the naphthalene nucleus and include the desired 2,6- and 2,7- dimethylnaphthalenes. These compounds, along with the dimethylnaphthalenes from the fresh charge and ethylnaphthalenes, constitute the major part of the product removed from the bottom of column 15 via line 16.

This material is sent through line 35 to a fractionation section indicated by columns as and 37. In column 36 material distilling below 500 F. and composed mainly of methylnaphthalenes and a small amount of ethylnap thalenes is distilled over head and passes through lines 38 and 20 to the dealkylator. Material boiling above 520 F. is rejected from the bottom of tower 36 via line 39. An intermediate fraction boiling SOD-520 F. and composed of dimethylnaphthalenes and generally a small amount of ethylnaphthalenes is taken through line 40 to tower 37. Therein a sharp fractionation is effected to remove overhead in line 41 a SOD-510 F. cut and leave a bottom product of 5l0520 F. boiling range. It has been found that with sufficiently good fractionation substantially all of the 2,6- and 2,7-dimethylnaphthalenes that were present in the fresh charge and that were produced by cracking the diarylmethanes in zone 13 will appear in the SOD-510 F. overhead cut. The bottom fraction, which is composed of other dimethylnaphthalenes (mainly the 1,3-, 1,6- and 2,3-isomers), passes through lines 42 and 20 to the dealkylator.

The SOD-510 F. cut from line 41 will contain, in addition to substantially all of the 2,6- and 2,7-isomers, substantial amounts of the 1,3-, 1,6- and 1,7-isomers and generally a small amount of ethylnaphthalenes. These other components all have freezing points considerably lower than the 2,6- and 2,7-isomers. Hence the cut is passed to crystallizer 43 and a separation is made by fractional crystallization. The 2,6- and 2,7-dimethylnaphthalene concentrate obtained as indicated by line 44 can further be resolved into a 2,6-concentrate and 2,7-concentrate, for example, by suitable fractional crystallization procedure such as is disclosed in Robinson application U.S. Serial No. 857,448, filed December 4, 1959. The filtrate from crystallizer 43, containing the other isomers, is passed through lines 45 and 20 as part of the feed to the dealkylator.

From the foregoing description, it can be seen that the present process is capable of producing 2,6- and 2,7- dimethylnaphthalenes in quantities greater than the amounts that these constituents occur in the charge to the process, and further that the process is capable of converting all the other alkylnaphthalenes in the charge to naphthalene.

I claim:

1. In a process involving hydrodesul'turizing a gas-oil fraction boiling mainly in the range of 440-525 F. and containing mainly monocyclic and dicyclic aromatic hydrocarbons including dimethylnaphthalenes, separating from the desulfurization product material containing methylnaphthalenes, subjecting such material to a dcalkylation reaction in the presence of added hydrogen as the sole source thereof at a temperature above 1000 P. to produce naphthalene and recovering from the deaikylation product naphthalene and a recycle fraction rich in monomethylnaphthalene, the steps for producing and recovering 2,6- and 2,7-dimethylnaphthalene which comprises: (1) reacting said recycle fraction with formaldehyde in the presence of an acid catalyst to form diarylmethanes; (2) introducing the reaction product along with said gas-oil fraction to the hydrodesulfurization zone to crack the diarylmethanes; (3) separating from the hydrodesulfurization product a fraction boiling essentially in the range of 500-510 F. and containing a major amount of dimethylnaphthalenes; (4) fractionally crystallizing the 500-510 F. fraction to separate 2,6- and 2,7-dirnethylnaphthalenes from other dimethylnaphthalenes; and (5) passing the filtrate from step (4) and materials from step (3) boiling below 500 F. and above 510 F. to said dealkylation reaction for conversion to naphthalene.

2. Process for the production of naphthalene and a concentrate of 2,6-dimethylnaphthalene and 2,7-dimethylnaphthalene from cracked petroleum fractions which comprises:

(a) extracting said cracked petroleum fraction with a solvent to produce an aromatic extract containing mainly monocyclic and dicyclic aromatic hydrocarbons including dimethylnaphthalenes;

(b) passing said extract together with a hereinafter specified condensation product into a catalytic desulfurization zone at a temperature of 800-980 F., pressure of 150-1000 p.s.i.g., hydrogen to hydrocarbon mole ratio of 3 :1 to 25:1, and liquid hourly space velocity of 05-10, suflicient to efiect cracking of the saturates, monocyclic aromatics and said condensation product, and to convert sulfur to hydrogen su fide,

(c) separating from the desulfurization product material containing methylnaphthalenes;

(d) subjecting said material to a dealkylation reaction in the presence of added hydrogen as the sole source thereof at a temperature above 1000 F. to produce naphthalene in high concentration;

(e) recovering naphthalene from the dealkylation product;

(f) removing a recycle fraction rich in monomethylnaphthalene from the dealkylation product;

(g) reacting said recycle fraction with formaldehyde in the presence of an acid catalyst to form a condensation product containing diarylmethanes;

(h) recycling said condensation product to step (b);

(i) separating from the desulfurization product a fraction boiling essentially in the range of 500--510 F. and containing a major amount of dirnethylnaphthalenes;

(j) subjecting said 500-510 F. fraction to fractional crystallization to separate 2,6- and 2,7-dimethylnaphthalene from other dimethylnaphthalenes;

(k) recovering a concentrate of 2,6- and 2,7-dimethylnaphthalene from the crystallization product; and,

(I) passing the filtrate from step (j) and materials from step (i) boiling below 500 and above 510 F. to said dealkylation reaction.

3. Process according to claim 2 wherein said extract is a catalytic gas oil fraction boiling in the range of 440- 525 F. containing a major proportion of dicyclic aromatic hydrocarbons.

4. Process according to claim 3 wherein said dealkylation reaction is effected thermally without a catalyst at a temperature of i200-1400 F, pressure of -1000 p.s.i.g., hydrogen to hydrocarbon mole ratio of 3:1 to 25:1, and a residence time of 2-300 seconds.

5. Process according to claim 1 wherein said gas oil fraction is catalytic gas oil.

6. Process according to claim 1 wherein said dealkylation reaction is effected thermally without a catalyst at a temperature of 12001400 F., pressure of 150-1000 p.s.i.g., hydrogen to hydrocarbon mole ratio of 3:1 to 25: 1, and a residence time of 2-300 seconds.

References titted in the file of this patent UNITED STATES PATENTS 2,577,788 McAteer et al Dec. 11, 1951 2,897,245 Fetterly July 28, 1959' 2,920,115 Friedman Jan. 5, 1960 2,981,765 Fetterly Apr. 25, 1961 3,001,932 Pietsch Sept. 26, 1961 

1. IN A PROCESS INVOLVING HYDRODESULFURIZING A GAS-OIL FRACTION BOILING MAINLY IN THE RANGE OF 440-252*F. AND CONTAINING MANLY MONOCYCLIC AND CICYCLIC AROMATIC HYDROCARBONS INCLUDING DIMETHYLNAPHTHALENES, SEPARATING FROM THE DESULFURIZATION PRODUCT MATERIAL CONTAINING METHYLNAPHTHALENES, SUBJECTING SUCH MATERIAL TO A DEALKYLATION REACTION IN THE PRESENCE OF ADDED HYDROGEN AS THE SOLE SOURCE THEREOF AT A TEMPERATURE ABOVE 1000*F. TO PRODUCE NAPHTHALENE AND RECOVERING FROM THE DEALKYLATION PRODUCT NAPHTHALENE AND A RECYCLE FRACTION RICH IN MONOMETHYLNAPHTHALENE, THE STEPS FOR PRODUCING AND RECOVERING 2,6- AND 2,7-DIMETHYLNAPHTHALENE WHICH COMPRISES: (1) REACTING SAID RECYCLE FRACTION WITH FORMALDEHYDE IN THE PRESENCE OF AN ACID CATALYST TO FORM DIARYLMETHANES; (2) INTRODUCING THE REACTION PRODUCT ALONG WITH SAID GAS-OIL FRACTION TO THE HYDROSELFURIZATION ZONE TO CRACK THE DIARYLMETHANES; (3) SEPARATING FROM THE HYDRODESULFURIZATION PRODUCT A FRACTION BOILING ESSENTIALLY IN THE RANGE OF 500-510*F. AND CONTAINING A MAJOR AMOUNT OF DIMETHYLNAPHTHALENES; (4) FRACTIONALY CRYSTALLIZING NAPHTHALENES FROM OTHER DIMETHYLNAPHTHALENES; AND (5) PASSING THE FILTRATE FROM STEP (4) AND MATERIALS FROM STEP (3) BOILING BELOW 500*F. AND ABOUT 510*F. TO SAID DEALKYLATION REACTION FOR CONVERSION TO NAPHTHALENE. 